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Dictionary of the History of Ideas

Studies of Selected Pivotal Ideas
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1. Crises of the Chain of Being: The Controversies
over the Notion of Species.
We have said that for Kant
the empirical use of ideas such as that of continuity
and of the plenitude of forms (plenum formarum) was
illegitimate and could only make for contradictions and
controversies. His conclusion seems to be, and indeed
is, in part, a commentary on the eighteenth-century
discussions of continuity and plenitude in the biological

At first the new instruments of scientific research do
not seem to contradict the idea of a Scale of Creatures.
Indeed, the already widespread use of the microscope
makes it possible to observe the world of the infinitely
small; and in 1739 the discovery of Trembley's Hydra
is hailed as the discovery of the missing link between
the vegetable and animal worlds. Even the skeptical
“Pyrrhonism” of men of science, or their awareness
of the limitations of experimental research, echoes
Leibniz' vision of a universal “plenum” of which we
have a partial vision only. No, it is rather the debate
over the notion of biological species that challenges
the foundations of the Chain of Being, and in particular
the principle of plenitude. In order to salvage this
principle it was necessary to attribute only a conven-
tional, not real, value to biological classifications: sub-
division into species would in fact have created in
nature a too nicely spaced series, letting precisely those
imperceptible gradations escape which assure conti-
nuity and plenitude in the natural world.

The conventionality of species is affirmed in Buffon's
Discours sur la manière d'étudier et de traiter l'Histoire
which prefaces the first volume of his Histoire
(1748). The methods or “systems” of classifi-
cation are, to be sure, indispensable but artificial: as
against the nuances of natural reality we have an arbi-
trarily articulated series. The error of all classification
rests on the inability to grasp the processes of nature,
which are always realized by degrees, by imperceptible
nuances, thus escaping all division. In short, only indi-
viduals exist in reality; genera or species do not.

But Buffon wholly reversed his position in the course
of his research, prompted by the now general recogni-
tion of species as a genetic entity. In fact, in Volume
XIII of the same work (1765) he affirms that the only
true beings in nature are species and not individuals.

Robinet, a firm advocate of the principle of pleni-
tude, was quite clear about the dangers inherent in
classifications: if we accept the separation of nature
into orders of this kind, the Chain of Being is fatally


broken (De la nature [1766], IV, 4-5). Doubtless the
introduction of the idea of species as a genetic entity
contributed decisively to this crisis of the principle of
plenitude: since two individuals are said to belong to
the same species if they are capable of producing a
fertile offspring and of transmitting to it their own
hereditary characteristics, it is hard to imagine a “full”
concatenation among the diverse species. Actually, in
the second half of the eighteenth century, the notion
of species is already established and operative in the
biological sciences. The controversies—accelerated by
the always growing body of empirical data, and par-
ticularly by the data of the new science of paleon-
tology—had to do rather with the fixity or nonfixity
of the species (taken now as established entities).

2. Crisis of the Chain of Being: Permanence and
Becoming in Nature.
In a world hierarchically ar-
ranged, such as the one described by the great meta-
phor of a Chain or scale of beings, orders of creatures
had to be considered fixed ab aeterno with their essen-
tial and thus unalterable characteristics. In the third
decade of the century Réaumur wrote: “The author
of nature wanted our earth to be populated with a
prodigious number of species of animals, and has given
the earth those species fit for it to possess....” And
again: “One must start from the principle that the
species of insects are—no less than those of animals—
invariable in form” (Mémoires pour servir à l'histoire
des insectes
[1734-42], II, XL-XLI). The physician
Antonio Vallisnieri (1661-1730) affirmed on anatomical
grounds that it was impossible for carnivorous habits
to be acquired: it is no accident (only to regret it
afterward) that God, immutable and omnipotent,
wanted herbivores to be so different from carnivores:
such difference is but another proof of the unalterable
structure of that great theater that is nature (Opere
I, 315A). In general all adaptation phe-
nomena should be interpreted not as chance environ-
mental mutations but as providentially preordained
laws (ibid., I, 137B). The fixity of species is also basic
to Linnaeus' Philosophia botanica (1751).

Faith in the permanence of nature (required by the
idea of the Chain of Being) and the affirmation that
there is evolution in nature are clearly contradictory:
mediating between them was a theory of the preexis-
tence of seeds—already diffuse, beginning from the last
decades of the seventeenth century—according to
which every living thing would exist already formed
in all its parts in the seed, and all seeds, created ab
would simply be transmitted and developed in
reproduction. With such a doctrine—adopted by Fon-
tenelle and Leibniz among others—one could conceive
of the history of nature as explication and development
of all those possibilities already foreseen ab aeterno as
essential parts of the world's structure.

This transformist view afforded a reconciliation of
the idea of plenitude with that of the perfectibility
of nature. And in this sense it is used, for example,
by Robinet in his De la nature (1761-68). In a word,
natural development, if seen as development of matu-
ration of preexisting seeds, adds nothing really new to
creation but simply explicates its original productivity.
Nature is continuously working itself out, and the
principle of plenitude is manifest in this temporal

Yet just this transformism was bound to challenge,
explicitly or implicitly, the notion of the fixity of spe-
cies and thus precipitate a crisis in the hierarchical
image of the cosmos. But for that matter numerous
and grave objections to the fixity of species were being
raised by the necessity to give some plausible account
of hereditary and adaptation phenomena, which re-
quire the intervention of variation and of environ-
mental determination. Remarkable how Maupertuis in
his Essai de cosmologie (1750), precisely by reflecting
upon adaptation phenomena and the natural selection
that implies, was led to draw the same conclusion that
Kant was to draw some years later, in regard to the
illegitimacy of the empirical use of the principles of
plenitude, of homogeneity, and of continuity. Only
those species that have certain adaptable relations
(rapports de convenance) with nature may survive.

One would say that chance has produced an incalculable
multitude of individuals; a small number happened to be
so constructed that the parts of each creature were capable
of satisfying its needs; in another number, infinitely larger,
there was neither adaptability nor order; such species have
all perished... and the species that we see today are the
tiniest part of all a blind destiny has produced

(Essai, in
Oeuvres [1756], I, 11-12).

The continuity of the natural world can never be, then,
an empirical statement: uniformity is (as we may say)
a spiritual exigency and has no exact counterpart in
experience: Continuity pleases our mind, but does it
please Nature? (Elle plaît à notre esprit, mais plaît-elle
à la Nature?
—ibid., 51). The Chain of Being, thanks
to which we may imagine a universe so constituted
that the beings that fill it can only be the perfectly
juxtaposed parts of the whole, was perhaps broken up
by some telluric cataclysm; however that may be, it
cannot now be reconstructed on the basis of observa-
tion. And it is for this reason that Maupertuis, in the
third part of his Essai, presents it as pure conjecture.

But even more telling than Maupertuis' Essai of the
new philosophy of nature is his Système de la nature
(first ed., in Latin, 1751), wherein we witness the disso-
lution of that bond between natural forms and divine
creativity which had, from the Timaeus on, formed the
basis of the Chain of Being. To suppose that all indi-


viduals were made by the divine will on one and the
same day of creation, says Maupertuis, means to have
recourse to a miraculous rather than physical explana-
tion. The laws at work in nature, which are the only
object of science, operate to conserve and also to
transform natural forms (French edition [1756], sec-
tions XI-XLIX).

The importance of this new conception of the rela-
tions between God and nature is certainly the decisive
element in the dissolution of the Chain of Being. As
Roger has observed ([1963], pp. 486-87), Maupertuis,
rejecting the preexistence of seeds, the notion of God
as “maker,” and the fixity of forms, was led to study
the life of natural forms in time, introducing duration
into biological sciences as an essential element. This
general temporalization of nature is a particular exam-
ple of what Lovejoy has called ([1936], p. 242) the
“temporalizing” of the Chain of Being. According to
the traditional conception, the Scale of Creatures was
static and the temporal process brought no enrichment.
In the new “temporalized” version the plenum for-
was conceived instead “not as the inventory
but as the program of nature, which is being carried
out gradually and exceedingly slowly in cosmic history”
(ibid., p. 244).